International Journal of Scientific & Engineering Research, Volume 3, Issue 11, November-2012 1

ISSN 2229-5518

Behavior of Integral Abutment Bridge with and without Soil Interaction

R.Shreedhar, Vinod Hosur, Iftikar Chappu

Abstract— Integral Abutment bridges (IAB’s) can be defined as bridges without joints. The main purpose of constructing IAB’s is to pre- vent the corrosion of the structure due to water seepage through joints. The biggest uncertainty in the design of these bridges is the re- action of the soil behind the abutments and next to the foundation piles, especially during thermal expansion. This lateral soil reaction is nonlinear and is a function of the magnitude and nature of the wall displacement.To gain a better understanding of the mechanism of load transfer due to thermal expansion, which is also dependent on the type of the soil adjacent to the abutment walls and piles, a 3D fi- nite element analysis is carried out on representative IAB. In this paper two models are compared one with considering soil interaction and other without soil interaction and live load is applied using STAAD-Beava. The main objective is to study the trends in bending mo- ment, shear force and deflection in central and end longitudinal girders and deck slab due to dead load, live load in combination of thermal loads. This paper emphysis that the temperature effects are more significant in case of integral abutment bridges, however the changes in soil properties behind the abutment and around the piles do not affect significantly the performance of super structure.

Index TermsAbutment, Deck, Integral Bridge, Piles, Soil interaction, Springs, Thermal stresses.

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1 INTRODUCTION

NTEGRAL Abutment bridges (IAB’s) are the bridges with- out joints. Bearings and expansion joints are the weak links in a bridge. Hence, interest in integral bridges or joint less
bridge is increasing and their performance has gained interna-
tional attention. The main purpose of constructing IAB’s is to prevent the corrosion of the structure due to water seepage through joints. The simple and rapid construction provides smooth, uninterrupted deck that is aesthetically pleasing and safer for riding.

The continuity achieved by this construction results in thermally induced deformations. These in turn introduce a significantly complex and non-linear soil structure interac- tion into the response of abutment walls and piles of the IAB. The unknown soil response and its effect on the stresses in the bridge, creates uncertainties in the design.

To gain a better understanding of the mechanism of load transfer due to thermal expansion, which is also dependent on the type of the soil adjacent to the abutment walls and piles, a 3D finite element analysis is carried out on representative IAB using software STAAD ProV8i and live load was introduced as per IRC-6(2000) using STAAD-Beava (Bridge Engineering Automated Vehicle Application). The nonlinear soil behaviour is handled using multilinear springs at the abutment wall and pile nodes. The nonlinear soil springs behind the walls are the force-deflection design

curves recommended in the National Cooperative High- ways Research Program (NCHRP 1991) design manual. The nonlinear p-y design curves recommended by the American Petroleum Institute (API 1993) are used adjacent to the piles.

2 NUMERICAL EXAMPLE:


The objective of the present work is to study the behaviour of the integral bridge under various load combinations of dead load, live load and thermal loads varying from 100C to 500C with 10ºC rise with each load case applied throughout the bridge deck in the longitudinal direction. The live load is ap- plied as per IRC 6- 2000 using STAAD-Beava (Bridge Engi- neering Automated Vehicle Application). Here the software automatically calculates the vehicle load and no of lanes de- pending upon the carriage way width as per the codal provi- sion.

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 Prof. R. Shreedhar is associate professor in the Department of Civil engineering in Gogte Institute of Technology Belgaum (Karnataka), INDIA, PH:+919845005722. E-mail: rshree2006@gmail.com

 Dr.Vinod Hosur Professor in the Department of Civil Engineering at Gogte Institute of Technology Belgaum (Karnataka), INDIA, Ph:+919448193110. E-mail: vinod.hosur@gmail.com

 Iftikar S Chappu is currently pursuing master degree in Structural engineering at Gogte Institute of Technology Belgaum (Karnataka), INDIA, PH:+919742084390. E-mail: iftikar.sc@gmail.com

Fig. 1. Picture showing the model of IAB

Deck Slab:- Length:74 mt; Width:12mt; Thickness:0.24mt Abutment:- Height 2.5mt; Width:12mt; Thickness:1.25mt Girders:- Longitudinal girder: 5 nos (0.35mt X 1.5mt)

Cross girder: 4 nos (0.5mt X 1.0mt)

Piles:- Nos 7; Height: 5.1mt

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3 STRUCTURAL AND MATERIAL MODELLING OF AN

INTEGRAL BRIDGE

The structural elements of the bridge are modeled as linear elements while the soil reaction adjacent to the piles and be- hind the abutment walls are modeled as nonlinear support springs. The 3D model of the structure comprises of:
i. The superstructure consisting of concrete slab acting in composition with five longitudinal girders and four cross beams, one at each end of span.
ii. The deck slab is modeled using plate elements and the girders as beam elements. The intermediate piers being treated as simple roller supports.
iii. The 2.5 m high abutment modeled as plate elements.
The soil behind the abutment and around the piles modeled as multilinear springs.
iv. Seven steel piles with full fixity are connected to each abutment walls, allowing full moment transfer. Each pile is modeled as beam element with common node for pile and the abutment wall using structural analy- sis software, STAAD.Pro V8i.

4 CALCULATION OF SPRING STIFFNESS FOR

ABUTMENT AND PILES

4.1 Spring Stiffness Calculations for Abutment

NCHRP curves relate the horizontal normal stress σ’h to the vertical effective normal stress σ’v according to σ’h = K σ’v where for a uniform density dry soil σ’v = γz, where γ = dry density of soil.
To calculate the effective soil spring resistance for input

into the bridge model, the effective panel size of each wall el- ement is computed using dimension as used in the model. Typical interior panels are of width w =2m and height h= 0.5m. this area is multiplied by the effective vertical normal stress σ’v for a given panel depth z and by the lateral earth pressure co-
F= force in spring
pu = ultimate soil resistance (lower of pus or pud)
pus = shallow ultimate resistance pud = deep ultimate resistance
k1 = initial soil stiffness chosen for a given of friction Φ
z = soil depth from the bottom of approach slab to the spring y = horizontal displacement
Lp = length of beam element
The ultimate soil resistances are given as pus = ( c1 z + c2 D) γ’ z
pud= c3 γ’ D z
where,
γ’ = dry density of soil adjacent to piles
Φ = angle of internal friction in sand
c1, c2, and c3 are coefficients as functions of Φ, and
D = average pile diameter from surface to depth (length).
c1 = k0 tan() sin  / tan( - ) cos() + tan2  tan() / tan(-) +
k0 tan (tan() sin  - tan())
c2 = tan  / tan (-) – tan2 (45- / 2)
c3 = k0 tan () tan4  + ka (tan8-1)
= Φ/2
β= 45 + Φ/2
ko= at rest earth pressure coefficient = (1- sinΦ)
ka= Rankine active earth pressure coefficient = tan2 (45- Φ/2)
Initial stiffness of soil= k1
Dry density of soil adjacent to piles = γ’

5 RESULTS AND DISCUSSION

The results are compared for the bending moments, deflection and shear force for the central and end longitudinal girder and deck slab and are presented in the form of graphs considering the effects of soil for IAB’s.
efficient K for a given deflection to yield a lateral force – deflection curve for a given node F = K σ’v w h (6) Where σ’v = γz
σ’v = vertical normal stress z = panel depth
w = width of plate as used in model h= height of plate as used in model
K=Earth pressure coefficient versus relative wall displacement

4.2 Spring Stiffness Calculation for Piles


As earlier stated the soil resistance p is given by equation
And the force-displacement relation is given by

10

0

-10

-20

-30

-10 0 10 20 30 40 50 60 70 80

Distance from left end Abutment (Mt)

DL

DL + 10*C DL + 20*C DL + 30*C DL + 40*C DL + 50*C


Where,

(6)

Fig. 1. Deflection in central longitudinal girder due to dead load +

thermal load combination of IAB with soil interaction

A= 0.9 is introduced for cyclic loading (= 3.0 − 0.8 (z/D) ≥ 0.9)

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2000

1000

DL

DL + 10*C DL + 20*C DL + 30*C DL + 40*C DL + 50*C

There is significant variation in bending moment in the longitudinal girder due to increase in temperature. The maxi- mum percentage variation in bending moment due to Dead load + Thermal load for IAB with soil interaction is obtained to be around 14% for 100C and 68% for 500C. (Fig 2)

0

-1000

-10 0 10 20 30 40 50 60 70 80

Distance from left end Abutment (Mt)

Dead load + Thermal load for IAB with soil interaction is ob- tained to be around 2.4% for 100C and 12% for 500C. (Fig 3)
The maximum percentage variation in bending moment in deck slab due to Dead load + Thermal load for IAB with soil interaction is obtained to be around 14% for 100C and 71% for

Fig. 2. Bending moment in central longitudinal girder due to dead load + thermal load combination of IAB with soil interaction.

Without Sub Soil Interaction

0

400

200

DL

DL + 10*C DL + 20*C DL + 30*C DL + 40*C DL + 50*C

-10

-20

-30

0

-40

-200

-50

-10 0 10 20 30 40 50 60 70 80

Distance from left end Abutment (Mt)

-400

-10 0 10 20 30 40 50 60 70 80

Distance from left end Abutment (Mt)

Fig. 3. Shear force in central longitudinal girder due to dead load +

thermal load combination of IAB with soil interaction.

3000

With Sub Soil Interaction

Without Sub Soil Interaction

DL

DL + 10*C

20 DL + 20*C DL + 30*C DL + 40*C DL + 50*C

10

2000

1000

0

-1000

0

-2000

-10

-10 0 10 20 30 40 50 60 70 80

Distance from left end Abutment (Mt)

0 10 20 30 40 50 60 70 80

Distance from left end Abutment (Mt)

tion

The variation of bending moment, shear force and deflection in longitudinal girders is found to increases with increase in temperature.
The maximum percentage variation in Deflection in longi-
tudinal girder due to Dead load + Thermal load for IAB with


The reduction in the maximum deflection due to Dead load +
Live load in the girders for the IAB without soil interaction as
compared to IAB with soil interaction are 2.54% & 4.02% for end & central longitudinal girder respectively. (Fig 5)
The maximum positive moments due to Dead load + Live load in the girders for the IAB without soil interaction are

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slightly lower than the IAB with soil interaction. For the two

bridges considered in the study, the reduction in the maxi- mum positive moment are 1.57% and 2.47% for end & central longitudinal girder respectively. (Fig 6)
load in the Deck Slab for the IAB without soil interaction are
slightly lower than the IAB with soil interaction. For the two bridges considered in the study, the reduction in the maxi- mum positive moment in the bridge deck is 2.27%. (Fig 8)

600

With Sub Soil Interaction

Without Sub Soil Interaction

400

200

0

-200

-400

-600

-10 0 10 20 30 40 50 60 70 80

Distance from left end Abutment (Mt)

Fig. 9. Percentage variation of Deflection, SF & BM of IAB with soil interaction for Dead Load and Combination of Thermal Load.

30 With Sub Soil Interaction

Without Sub Soil Interaction

20

10

0

-10

-20

-30

0 10 20 30 40 50 60 70 80

Distance from left end Abutment (Mt)

Fig. 10. Percentage variation of Deflection, SF & BM of IAB without soil interaction for Dead Load and Combination of Thermal Load.


The reduction in the maximum deflection due to Dead load +
Live load in the girders for the IAB without soil interaction as compared to IAB with soil interaction are 2.54% & 4.02% for end & central longitudinal girder respectively. (Fig 5)
The maximum positive moments due to Dead load + Live load in the girders for the IAB without soil interaction are slightly lower than the IAB with soil interaction. For the two bridges considered in the study, the reduction in the maxi- mum positive moment are 1.57% and 2.47% for end & central longitudinal girder respectively. (Fig 6)
There is negligible difference in the maximum Shear Force
due to Dead load + Live load in the girders for the IAB with- out soil interaction as compared to IAB with soil interaction i.e. 0.14% & 0.72% for end & central longitudinal girder re- spectively. (Fig 7)
The maximum positive moments due to Dead load + Live

Fig. 11. Percentage variation of deflection, SF & BM of IAB with soil

interaction for dead load + live load and Combination of Thermal

Load.

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Fig. 12. Percentage variation of deflection, SF & BM of IAB without soil interaction for dead load + live load and Combination of Ther-

mal

TABLE 2

PERCENTAGE CHANGE FOR IAB WITH SOIL INTERACTION WITH RESPECT TO IAB WITHOUT SOIL INTERACTION FOR DEAD LOAD + LIVE LOAD CONDITION

TABLE 1

PERCENTAGE CHANGE FOR IAB WITH SOIL INTERACTION WITH RESPECT TO IAB WITHOUT SOIL INTERACTION FOR DEAD LOAD

CONDITION

There is slight increase in deflection, shear force and bending
moments (both positive and negative) in longitudinal girders
and deck slab for IAB with soil interaction compared to IAB without soil interaction for both the dead load and live load condition given in table 1 and 2.

6 CONCLUSIONS

Following are the conclusions based on the study:
1) The maximum deflection in longitudinal girder of integral
abutment bridge (IAB) is observed to be more when soil interaction is taken into account for all temperature ranges studied. Similar are the observations for shear force and bending moment in deck slab. This is due to effect of re- straint provided by stiffness of soil behind the abutment and around the piles.
2) There is no significant variation in bending moment, shear force and deflection in the longitudinal girder and deck slab for a particular temperature change for IAB with and without soil interaction.
3) It is observed that by changing the soil properties behind the abutment and around the piles does not affect signifi- cantly the performance of deck slab in terms of bending moment, shear force and deflection.
4) The bending moment and deflection in deck slab and
girders increases linearly with increase in temperature.
5) The moments on deck slab increase with increase in tem- perature for integral abutment bridges.

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